I was in the shower, and I heard the dogs barking at the back door.
I knew they needed to go outside, but I didn't want to get out.
I was pretty worried when they had stopped barking, because I figured I may have waited too long, and one had an accident.

I was prepared to clean up a mess thinking, well it was my bad, I forgot to let them out.

I walked over to the back door, and saw that it had been opened.

There is no one home, and I know no one gets hone until late evening, and it was about 1:30 or 2:00.

No one had come in the house, or I would have heard them.

I remember the back door was closed, because I went to check the weather, which by the way, is very nice! :)

I closed it, and made sure it was closed before I left.

It was still slightly cold then, so I didn't want to let out any heat.

I don't think this is anything that is supernatural. Unlike what Hollywood depicts, most spirits etc. don't have that much energy to be tangible with our physical world, at least not so simply.
Perhaps the dogs were able to move the door or the door wasn't shut properly and could have been opened by the wind. If not I would be more concerned about other things.
Check the door and see if the lock or latch is working properly. Or question anyone else who lives in the same house as you.